Electric lamp



April 8, 1941. L. J. DAVIES 2,237,754

ELECTRIC LAMP Filed Oct. 18, 1959 Inven'tov; Leonavd J. Davies,

His AHovney.

rented Apr. 8,1941

ELECTRIE Y Leonard John Davies, Rugby, England, assior to General Electric Comp a corporation or New York Application @eteher 1%, i939, @hl'lhll l lo. EWMH In Great Britain October 3, 193% (ill. ill-'39) it We.

This invention relates to electric lamps and more particularly to electric discharge lamps of the type in which a proportion of the energy supplied is given out as non-visible rays some of which are ultra-violet rays. It is well known that such rays can be converted into luminous rays and therefore made to increase the efliciency or the lamp for illuminating purposes, by causing the ultra-violet rays to be intercepted by a luminescent powder, and in such lamps it is necesnary to secure a layer or the luminescent material to the glass wall which encloses the are or the are tube.

lit is known-that this may be done by the use or hinders and vehicles such as sodium silicate or ultra-cellulose. If these are used the powder may be either mixed with the binder before applicatlon or -deposited on to the surface of a binder which has previously been applied to the while it is still tacky. With any of these ethods of application a normal part of the process is to heat the glass surface after the poweither by some. chemical union with the glass or by a physical contact such that the powder particles actually become embedded in the glass.

no object or my invention is to provide an economical method of applying the powder which obviates a second heating of the glass and the use oil a temporary binder.

Further objects and advantages of my inventron will appear from the following description ol'specles thereof and from the accompanying V dra inwhich:

Fla. 1 is a fragmentary sectional view of apparatus employed in practicing the method comprising my invention; and Fig. 2 is a similar view or a modified form of apparatus used in practicinw the method comprising my invention.

re invention consists in depositing the lumihescent powders on the glass as it is being formed while still in the molten state in the form of tubina. According to the present invention, luminescent powder it of a suitable grain size a blown in with the air stream through the hollow mandrel. The powder particles, on coming into contact with the molten or semi-molten surface of the glass, adhere thereto.

Owing to the fact that the tubing is for some distance after leaving the mandrel still elongating, it may be necessary to project into the tub ing through the hollow mandrel a secondary tube it, as shown in Fig. 2, through which the luminescent powder it is blown. This secondary tube would project to such a point that any alteration in diameter of the tubing or elongation of it after that point would not result in unwanted reduction or increase of the number of powder particles per unit area.

Tubing thus internally coated wouldbe cut to the desired length in the normal way, and because of the method of manufactura'the complete length of tubing would be coated with powder which is contrary to the present normal practice. Owing to the necessity of sealing in to the tube lengths, after cutting, may be raised Ito-such a temperature that the glass for a suitableidis tance from the ends becoznes.,molten. manner, any powder particles on the inner surface of the molten glass are removed either by chemical,decomposition or by complete absorption into the glass. It is understood, of course,

- notallowed: to distort in' 'such'a way that electhat during this process the ends of the tube are trodes could not be introduced. 7 p

In preparing lamp length'sjin the above manher the electrode sealing-in machine, and the into tubing from the melt of glass. In particular we form the tubing in a modified form of the well own Danner glass tube-maklng-machine.

in hlnes of this type molten glass IQ is al-' low to wrap itselt around a downwardly inced revolving hollow mandrel l I through which air can be blown in the direction indicated lamp exhaust oven, may be arranged adjacent to the cutting 011- point of the tube drawing machine, so that the glass is not allowed to cool before it is on the exhaust pumps. In this way some part at least of the normal oven heating and moreover the possibility of contamination of the powder by dust and atmospheric influences, is avoided.

- What I claim as new and desire to secure by letters Patentof the United States is:

'1. The method of applying a coating of luminescent powder to the inner wall or a glass tube by the arrow, and the glass leaves the mandrel which consists in blowing the powder into the tube while it is being drawn and is still in a molten condition.

2. The method of applying a coating of luminescent powder to the inner wall of a glass tube which consists in blowing into the tube th luminescent material entrained in a gaseous medium while the said tube is being drawn and is still in a molten condition.

3. The method of applying a coating of luminescent powder to the inner wall of a. glass tube which consists in blowing the powder into the tube while it is being drawn, at a point where the glass tube is still in a molten condition but has undergone substantially the greatest portion of its elongation.

LEONARD JOHN DAVIES. 

